The popular Latin phrase or expression is derived from Latin, literally meaning the former, from the word 'priori'.
It is based on theory or hypothesis rather than experiment. Something that is derived by logic, without observed facts.
Example: "An a priori judgment is not supported by fact."
The expression 'a priori' was used by Rene Descartes in his Principles of Philosophy. Rene Descartes has been dubbed the "Father of Modern Philosophy" and the "Father of Modern Mathematics."